Molecular sieves are a commercially important class of crystalline materials. They have distinct crystal structures with ordered pore structures which are demonstrated by distinct X-ray diffraction patterns. The crystal structure defines cavities and pores which are characteristic of the different species.
Molecular sieves are classified by the Structure Commission of the International Molecular sieve Association (IZA) according to the rules of the IUPAC Commission on Molecular sieve Nomenclature. According to this classification, framework type molecular sieves and other crystalline microporous molecular sieves, for which a structure has been established, are assigned a three letter code and are described in the “Atlas of Molecular sieve Framework Types,” Sixth Revised Edition, Elsevier (2007).
ERI framework type materials are characterized by three-dimensional 8-membered-ring pore/channel systems containing double-six-rings (d6R) and cages. Small pore molecular sieves containing d6R building units and cages have shown utility in methanol-to-olefins catalysis and in the selective catalytic reduction of nitrogen oxides (NOx) to name some of the more important commercial applications.
ERI framework type molecular sieves are often intergrown with offretite (OFF) framework type molecular sieves, a topologically related molecular sieve. Intergrown ERI/OFF molecular sieves comprise regions of ERI framework type sequences and regions of OFF framework type sequences. There are number of references which disclose materials that are intergrowths of ERI and OFF. Molecular sieve T is disclosed in U.S. Pat. No. 2,950,952 and later discovered to be an ERI/OFF intergrowth (see J. M. Bennett et al., Nature, 1967, 214, 1005-1006). U.S. Pat. No. 3,699,139 discloses the use of a benzyltrimethylammonium cation to synthesize ERI/OFF intergrowth molecular sieves. U.S. Pat. No. 4,086,186 discloses using choline to synthesize ZSM-34 (an intergrowth). U.S. Pat. No. 4,503,023 discloses molecular sieves designated LZ-220 which are more siliceous forms of the known mineral erionite and its synthetic analog, molecular sieve T. M. L. Occelli et al. in Zeolites, 1987, 7, 265-271 disclose using templates designated DABCO(I) and DABCO(II) to synthesize ERI/OFF intergrowth molecular sieves.
U.S. Pat. No. 7,344,694 reports synthesizing an essentially pure ERI framework type molecular sieve designated UZM-12. UZM-12 is purported to have a Si/Al ratio of greater than 5.5. UZM-12 can be prepared as nanocrystallites having an average particle size of about 15 to about 50 nm and a spheroidal morphology. UZM-12 is synthesized via a charge-density mismatch approach whereby quaternary ammonium hydroxides are employed to solubilize aluminosilicate species, while crystallization inducing agents such as alkali and alkaline earth metals and more highly charged organoammonium cations are often introduced in a separate step.